Various types of electromagnetic fuel injectors are used in the fuel injection systems of internal combustion engines. Such injectors, as well as other solenoid controlled valve structures, have been used which have incorporated therein a solenoid armature that is located between the pole piece of the solenoid and a fixed valve seat whereby the armature operates as a valve member. Examples of such electromagnetic fuel injectors or solenoid controlled valve structures are described in U.S. Pat. Nos. 4,515,129 issued May 7, 1985 to Stettner and 4,572,436 issued Feb. 25, 1986 to Stettner et. al. The above identified patents show arrangements in which an armature/valve is biased to a normally closed position against a fixed valve seat by a spring member. The armature/valve is operable between a seated, sealing position against the valve seat and an open position against a pole piece of the solenoid for controlling flow through a flow passage in the valve seat.
It is desirable to precisely control the flow of fuel through the valve seat, and thus the injector, in order to meet performance requirements, as well as, emissions regulations for internal combustion engines. It is also desirable that, for a given application, all injectors will meter equivalent quantities of fuel to the engine cylinders upon application of a predetermined electrical input. As such, the injector flow curve must be adjusted to meet a given set of nominal flow requirements. In general the injector is a linear device that will meter fuel on a per-pulse basis which is proportional to the input. The specific relationship between pulse-width and fuel delivered is dependent upon the static flow of the injector, which is typically controlled through armature stroke, and dynamic response or flow, which is typically controlled through armature spring load. Setting the static and dynamic flow requirements in injectors has presented the manufacturer with concerns of contamination, durability and accuracy since calibration normally occurs during assembly, requiring further handling subsequent to flow adjustment.